The present disclosure relates to a sensing device, a power reception device, a power transmission device, a non-contact power transmission system, and a sensing method that sense the presence of a conductor such as a metal.
Recently, non-contact power transmission systems that supply (wirelessly transmit) power in a non-contact method have been actively developed. There are roughly two types of techniques among methods of implementing wireless power supply.
One technique is a well-known electromagnetic induction scheme. In the electromagnetic induction scheme, a degree of coupling between a power transmission side and a power reception side is very high and power can be supplied with high efficiency. However, because it is necessary to maintain a high coupling coefficient between the power transmission side and the power reception side, power transmission efficiency between coils of the power transmission side and the power reception side (hereinafter referred to as “efficiency between coils”) may be significantly degraded if the power transmission side is distant from the power reception side or there is a position gap.
The other technique is referred to as a magnetic-field resonance scheme, and has a characteristic that magnetic flux shared by a power supply source and a power supply destination may be lower because a resonance phenomenon is actively employed. In the magnetic-field resonance scheme, the efficiency between coils is not degraded if a Q value (quality factor) is large even when a coupling coefficient is small. The Q value is an index representing a relationship between energy retention and loss in a circuit having a coil of the power transmission side or the power reception side (indicating the strength of resonance of a resonant circuit). That is, there is a merit in that axial alignment of the coils at the power transmission side and the power reception side is unnecessary and a degree of freedom of positions or distances of the power transmission side and the power reception side is high.
In the non-contact power transmission system, one important element is a countermeasure against heat generation of metallic foreign materials. This is not limited to the electromagnetic induction scheme or the magnetic-field resonance scheme. There is a problem in that heat is generated due to an eddy current occurring in a metal if the metal is between the power transmission side and the power reception side when non-contact power supply is performed. To suppress this heat generation, many techniques for sensing metallic foreign materials have been proposed.
For example, a technique of determining the presence/absence of a metallic foreign material by finding a change in a parameter (a current, a voltage, or the like) when the metallic foreign material is put between the power transmission side and the power reception side has been proposed. In this technique, it is not necessary to impose design constraints and it is possible to suppress cost. For example, a method of detecting a metallic foreign material according to a degree of modulation during communication between a power transmission side and a power reception side in Japanese Patent Application Laid-Open No. 2008-206231 and a method of detecting a metallic foreign material according to eddy-current loss (foreign-material sensing based on direct current (DC)-DC efficiency) in Japanese Patent Application Laid-Open No. 2001-275280 have been proposed.